Powertrains having an internal combustion engine coupled to a continuously or infinitely variable transmission (CVT) may be employed to provide tractive effort in vehicles. A characteristic of a CVT includes the capability to continuously change a speed ratio between a minimum input speed/output speed (overdrive) ratio and a maximum input speed/output speed (underdrive) ratio, thus permitting selection of engine operating points that achieve peak efficiency, e.g., a mean-best torque point that is responsive to an operator torque request. As such, a continuously variable transmission is capable of steplessly changing through an infinite number of effective gear ratios over a range between a maximum gear ratio and a minimum gear ratio.
Known belt-type continuously variable transmissions include two pulleys, each having two sheaves. A continuous torque-transfer device, e.g., a belt runs between the two pulleys, with the two sheaves of each of the pulleys sandwiching the belt therebetween. Frictional engagement between the sheaves of each pulley and the belt couples the belt to each of the pulleys to transfer torque from one pulley to the other. One of the pulleys may function as a drive or input pulley so that the other pulley (an output or driven pulley) can be driven by the drive pulley via the belt. The gear ratio is the ratio of the torque of the driven pulley to the torque of the drive pulley. The gear ratio may be changed by moving the two sheaves of one of the pulleys closer together and the two sheaves of the other pulley farther apart, causing the belt to ride higher or lower on the respective pulley.
Known toroidal continuously variable transmissions include discs and roller mechanisms that transmit power between the discs. The toroidal continuously variable transmission includes at least one input disc rotatably coupled to a torque generator, e.g., an internal combustion engine, and at least one output disc rotatably coupled to the transmission output. The input disc and output disc define a cavity therebetween. The cavity defines a toroidal surface. The roller mechanism is placed within the cavity and is configured to vary the torque transmission ratio as the roller mechanism moves across the toroidal surface. A controlled tilt of the roller mechanism within the cavity changes the relative diameter of engagement of the input disc and output disc and incrementally changes the torque transmission ratio, providing for smooth, nearly instantaneous changes in torque transmission ratio.